The objective of this protocol is to study systematically in a quantitative manner the ocular motor subsystems in human subjects with clinically important disorders of eye movements in an attempt to improve diagnosis and understanding of pathophysiology of these disorders. Eye movements are recorded by electro-oculography and responses of the smooth pursuit, saccadic, optokinetic and vestibulo-ocular subsystems are analyzed with a laboratory computer. Eye movement disorders of present interest are: (1) congenital nystagmus, (2) myasthenia gravis, (3) cerebellar degenerations, and (4) congenital ocular motor apraxia.